A SNP in three different people, where each person has a different base at the same spot in the genome. The version of a SNP a person has is called their genotype, and these small genetic differences are part of what makes people unique. A spot in the genome that can differ between people (e.g., where some people have an A and others have a G) is called a single nucleotide polymorphism, or SNP (Figure 1). All humans share about 99.9% of this genome, and the remainder is variable (and 0.1% of 3 billion is still 3 million bases – nothing to sneeze at!).
In humans, the genome consists of 3 billion bases. A genome, in contrast, is a complete set of DNA instructions, including all of a person’s genes. A gene is a segment of DNA that contains instructions for one of these building blocks, such as a single protein. The order of these bases provides instructions for assembling the essential building blocks of life. It is made up of four types of smaller molecules, referred to as “bases”: adenine (A), thymine (T), cytosine (C), and guanine (G). DNA is a molecule that carries genetic information. DNA and the genome: a primerįirst, let’s talk a little bit about terminology. Since its completion in 2003, this project has laid the groundwork for thousands of scientific studies associating genes with human diseases. The Human Genome Project, one of the most ambitious scientific projects ever undertaken, achieved a monumental goal: sequencing the entire human genome.